The present disclosure herein relates to a semiconductor devices and, more particularly, to semiconductor devices that include field effect transistors and to methods for fabricating such devices.
Due to the advantages of their light weight, small size and/or low cost, semiconductor devices are widely used in numerous applications such as electronic devices, automobiles and/or ships. Field effect transistors (hereinafter also referred to as “transistors”) are one of the important constituent elements of many semiconductor devices. Typically, a transistor may include a source region (or “source”) and a drain region (or “drain”) which are spaced apart from each other in a semiconductor substrate, and a gate electrode that covers a channel region that is disposed between the source and the drain. The source and the drain may be formed by implanting dopant ions into the semiconductor substrate. The semiconductor substrate may be a bulk semiconductor substrate, a semiconductor on insulator substrate, a semiconductor epitaxial layer on a semiconductor or non-semiconductor substrate, etc. The gate electrode may be insulated from the channel region by a gate oxide layer disposed between the semiconductor substrate and the gate electrode. Such a transistor is widely used as a switching element and/or a logic circuit in a semiconductor device.
There is a constant demand for smaller and faster semiconductor devices. However, as size of a transistor is reduced, it can cause a decrease in the turn-on current for the transistor, which in turn may cause a decrease in the operation speed of the transistor. A decrease in the operation speed of the transistor may cause a decrease in the reliability of the semiconductor device and a decrease in the operation speed of the semiconductor device. Thus, research is being conducted on schemes for increasing the turn-on current for transistors that are used in highly-integrated semiconductor devices.